In recent years, attention has been paid to, as an input detection device, an input detection device having a touch detection function capable of detecting proximity (hereinafter, also including contact) of an external object, and such a device is called a touch panel. The touch panel is provided as a display device with a touch detection function, which is attached to or integrated in a display device, for example, a liquid crystal display device.
As an external object, for example, there is a touch panel enabling use of a pen. By using the pen, for example, a small area can be designated, or a handwritten character(s) can be inputted. There are various technologies for detecting a touch of the pen. One of the various technologies is an electromagnetic induction method. Since the electromagnetic induction method can realize high accuracy and high writing pressure detection accuracy, and can also realize a hovering detection function of detecting the external object separated from a touch panel surface, the electromagnetic induction method is a useful technology as a technology to detect the touch of the pen.
In addition, there is a touch detection device capable of detecting a finger(s) or the like as an external object. In this case, since a detection target is different from the pen, a method different from the electromagnetic induction method is adopted as a technology for detecting the touch. For example, there is a method for detecting an optical change, a change in a resistance value, or a change in an electric field caused by the touch of the finger or the like. Among these methods, the method for detecting the change in the electric field includes, for example, an electrostatic capacitance method using electrostatic capacitance. Since the electrostatic capacitance method has a relatively simple structure and has low power consumption, the electrostatic capacitance method is used for a personal digital assistant and the like.
Technologies related to the touch panel of the electromagnetic induction method are described in, for example, Patent Document 1 (Japanese Patent Application Laid-open No. 10-49301).